Barack Obama has significantly widened his lead over John McCain in Iowa since August, and the growing gap is linked to increased support from independents, a new analysis of last week's Big Ten Battleground Poll shows.

In the poll of 586 registered Iowa voters conducted Oct. 19-22, Obama led McCain by 13.5 points (52.4 percent to 39 percent with 5.5 percent undecided). His lead in Iowa is well outside the poll's 4.2 percent margin of error.

That means Obama has more than doubled his lead in Iowa since August, when a University of Iowa Hawkeye Poll showed him up by 6.4 points among registered voters (49.5 percent to 43.1 percent with 7.4 percent undecided).

Support among independent voters appears to be the reason Obama continues to increase his advantage in Iowa, said Hawkeye Poll Co-director Caroline Tolbert.

In the August Hawkeye poll, Iowa independents favored McCain. In the new Battleground Poll, Obama leads among Iowa independents by a 12.5 percent margin. Half of independents plan to vote for Obama, compared to 38 percent for McCain.

Obama has consistently led polls in Iowa since his unlikely but decisive victory in the Jan. 3 Iowa Caucuses served as a springboard for his White House bid.

"Obama's surprising win in Iowa -- a state that's 96 percent white -- proved to voters in other states he could win the nomination, creating the momentum that may have led to his eventual victory in the primaries," said Tolbert, an associate professor of political science in the UI College of Liberal Arts and Sciences. "Obama's successful bid for the Democratic nomination is rooted in the Iowa caucuses, and his support here remains quite strong."

Along with a widening margin in the polls, Obama received a higher favorability rating than McCain. Sixty-four percent of Iowans gave Obama a favorable rating, compared to McCain's 49 percent. Democratic vice presidential candidate Joe Biden was favorably rated by 57 percent of Iowans; only 44.5 percent gave Republican vice presidential candidate Sarah Palin a favorable rating.

"The negative advertising run by McCain in Iowa over the last few weeks may have contributed to his lower favorability rating," said UI political scientist and Hawkeye Poll Director David Redlawsk.

More than one-quarter of Iowa conservatives support Obama

Twenty-seven percent of Iowa voters who consider themselves conservative said they plan to vote for Obama while only 2 percent of liberals said they will support McCain. Conservatives outnumber liberals two to one in Iowa.

Obama leads among partisan voters in Iowa. Ninety-four percent of Democrats plan to vote for Obama but only 87 percent of Republicans plan to support McCain.

Obama's margin over McCain is greatest among young voters in Iowa. He holds a 35-point lead among voters ages 18-29. The Democrat also leads by 25 points among those 50-59 and 12 points among those 60 and older. McCain holds a four-point lead with the 30-39 age group; the candidates tied among Iowans ages 40-49.

"What appears to be underlying these numbers is the continued perception among Iowans that Obama can bring about change," Redlawsk said. "When asked which candidate can bring about change, 61.5 percent named Obama but only one-quarter said McCain."

McCain did, however, earn points for experience. Nearly three in four Iowa voters said McCain is the more experienced candidate; only 21 percent said Obama is.

"McCain may want to capitalize on this strength of experience in the final days before the election," Redlawsk said.

Financial crisis may have boosted Obama in Iowa

Sixty-one percent of Iowa voters said "economy and jobs" is the most important issue facing the country today. The next most frequently mentioned concern was "terrorism and national security," mentioned by 8.5 percent of those surveyed.

Ninety-two percent of Iowans believe the United States economy has gotten worse in the past year. But more than half of Iowans think the state economy improved in the same time period.

"Our August Hawkeye Poll was conducted before the financial crisis hit Wall Street; since then, the economic crisis appears to have significantly weakened support for the incumbent party, which has affected McCain's standings in the polls," Tolbert said.

About the Big Ten Battleground Poll

The Battleground Poll was co-directed by University of Wisconsin-Madison political scientists Charles Franklin and Ken Goldstein with the cooperation of colleagues from participating Big Ten universities. Polls were conducted in Ohio, Michigan, Pennsylvania, Indiana, Wisconsin, Iowa, Illinois and Minnesota, home to the 11 universities in the Big Ten Conference. The Iowa Big Ten Battleground Poll included 23 percent Republicans, 34.5 percent independents and 37 percent Democrats. Half of respondents were men; half were women.

For more details about the poll, its methodology, the show and a list of poll contacts at each of the participating universities, visit http://www.bigtenpoll.org.

For additional political news from the UI, a list of the university's political experts, and trading prices for Election 2008 contracts on the Tippie College of Business' Iowa Electronic Markets, visit http://www.uiowa.edu/election.